Recent years have seen rapid advancement in the field of wireless-communication technologies for use in consumer electronics and other devices. This advancement has been driven, at least in part, by demand for lower-cost, higher-performance wireless transceivers. Many advances in wireless transceivers have been enabled by improvements in complementary metal-oxide-semiconductor (CMOS) technologies. In fact, many components of wireless transceivers may now be integrated in CMOS chips, reducing the cost of wireless transceivers and, in turn, reducing the costs of the devices in which wireless transceivers are implemented. Scaled CMOS technology enables cost-effective full integration of single-chip radio systems as a result of its ability to simultaneously process analog, digital, and radio frequency (RF) signals. Although many sub-systems have been integrated in CMOS (e.g., Bluetooth, WLAN, and cellular telephone systems), the RF power amplifier has yet to be integrated in high-volume CMOS systems.
Power amplifiers have not been fully implemented in CMOS at least because it has proven difficult to achieve desirable operating characteristics of a power amplifier using CMOS technology. As an example of such operating characteristics, power amplifiers are typically required to operate at a sufficiently high output power level, have high energy efficiency, and exhibit sufficient linearity in amplification. The design of a given power amplifier system will require tradeoffs between these three parameters. However, inherent limitations of CMOS technology have limited the ability of CMOS-based designs to achieve desired combinations of such parameters.
Metal-oxide-semiconductor field-effect transistors (MOSFETs) are common in systems that are integrated in CMOS, including switching amplifiers in which MOSFETS are operated as binary switches. Such MOSFETS may play an important role, at least, in controlling the selection of the output voltages of the switching amplifier. The scaling of the minimum feature size and power-supply voltage in CMOS has enabled MOSFETs to switch at increasing speeds with decreasing dynamic power consumption, resulting in higher energy efficiencies. However, the associated lower operating voltage of such higher-efficiency MOSFETS may require the use of a higher impedance transformation ratio to produce a given output power. Further, the use of CMOS switches in power amplifiers typically requires additional circuits to, among other things, modulate output signal level. Such additional circuitry leads to complex designs that often require relatively large chip areas and relatively large amounts power consumption.
An improved power amplifier is therefore desired.